As is known in the art, the faculty of hearing entails not only detection, discrimination, and comprehension of acoustic sound signals, but also the ability to localize sound-emitting objects in space.
In this context, term localization encompasses the ability to determine direction of arrival (DOA) of the acoustic sound signal as well as the distance to a sound-emitting object. As is widely known, when the ear is occluded, for instance when a hearing protection earmuff or a headphone is employed, high frequency spectral cues, present in frequencies exceeding 1500 Hz and used for perception of auditory signal depth, are lost. High frequency spectral cues or pinna-based spectral cues, along with other important cues such as interaural intensity difference (IID) and interaural level difference (ILD), contribute to improve auditory localization of sounds as well as externalization of sounds. These pinna-based spectral cues are sometimes even called the directional transfer function (DTF). The DTF forms part of the head-related transfer function (HRTF), a well-known model for representing how an ear receives a sound from a point in space.
The purpose of a pinna (auricle, outer ear) is to guide and decode incoming acoustic sound signals. When the guiding/decoding function of the pinna is disabled, it has been proposed to use signal processing in order to restore this natural filtering performed by the pinna. However, these attempts have proven inadequate. Specifically, it is currently not feasible to, in real time, identify all possible sounds, both static and dynamic, present around the listener and filter each sound based on the personalized HRTF-characteristics of the listener.
On the above background, further attempts have been made to at least alleviate drawbacks associated with the art.
A general acknowledgement of the fact that the shape of the human pinna is of importance for the ability to determine the sound direction may be found in WO91/07153. In addition, WO91/07153 proposes to shape the outer surface of the ear covering member so as to very roughly imitate the main shape of the human pinna. Further, WO91/07153 teaches that the outer, imitated pinna should be larger than the natural pinna. Such an imitated pinna improves listener's ability to determine sound direction associated with the acoustic sound signal. However, the proposed teaching is ridden with considerable drawbacks. By way of example, its accuracy in determining various auditory parameters is inherently limited by its approximative design. Further and since the employed term “sound direction” is rather general, the majority of the parameters useful for sufficiently accurately determining the position of sound-emitting objects in space are not even considered by the disclosure.
On the above background, an objective at hand is to further improve the devices belonging to the state of the art.